Update CHANGELOG.md for 9.0.0

[ci skip]

changelogs/unreleased/27778-a11y-sidebar.yml

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-title: Improves a11y in sidebar by adding aria-hidden attributes in i tags and by
-  fixing two broken aria-hidden attributes
-merge_request:
-author:

changelogs/unreleased/27783-fix-fe-doc-broken-link.yml

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-title: Fixes FE Doc broken link
-merge_request: 9120
-author:

changelogs/unreleased/27840-improve-search-bar-experience.yml

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-title: Enhanced filter issues layout for better mobile experiance
-merge_request: 9280
-author: Pratik Borsadiya

changelogs/unreleased/27920-both-wip-messages-showing.yml

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-title: Dispatch needed JS when creating a new MR in diff view
-merge_request:
-author:

changelogs/unreleased/27924-set-max-width-mini-pipeline-text.yml

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-title: Set maximum width for mini pipeline graph text so it is not truncated to early
-merge_request: 9188
-author:

changelogs/unreleased/27934-left-align-logo.yml

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-title: Left align logo
-merge_request:
-author:

changelogs/unreleased/27936-make-all-uploads-require-revalidation-on-each-browser-fetch.yml

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-title: Uploaded files which content can change now require revalidation on each page load
-merge_request: 9453
-author:

changelogs/unreleased/27978-improve-task-list-ux.yml

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-title: Only add a newline in the Markdown Editor if the current line is not empty
-merge_request: 9455
-author: Jan Christophersen

changelogs/unreleased/27994-fix-mr-widget-jump.yml

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-title: Fix MR widget jump
-merge_request: 9146
-author:

changelogs/unreleased/28010-mr-merge-button-default-to-danger.yml

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-title: Default to subtle MR mege button until CI status is available
-merge_request:
-author:

changelogs/unreleased/28019-make-builds-show-faster.yml

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-title: Avoid calling Build#trace_with_state for performance
-merge_request: 9149
-author: Takuya Noguchi

changelogs/unreleased/28058-hide-emails-in-atom-feeds.yml

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-title: Only show public emails in atom feeds
-merge_request:
-author:

changelogs/unreleased/28082-deleted-branch-event-404.yml

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-title: Stop linking to deleted Branches in Activity tabs
-merge_request: 9203
-author: Jan Christophersen

changelogs/unreleased/28142-overlap-bugs.yml

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-title: Fix z index issues with sidebar
-merge_request:
-author:

changelogs/unreleased/28176_merge_widget_fix.yml

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-title: Fix error in MR widget after /merge slash command
-merge_request: 9259
-author:

changelogs/unreleased/28186-long-group-names-overflow-out-of-todos-view.yml

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-title: Truncate long Todo titles for non-mobile screens
-merge_request: 9311
-author:

changelogs/unreleased/28204-option-to-disable-webpack-dev-server-livereload.yml

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-title: Pick up option from GDK to disable webpack dev server livereload
-merge_request:
-author:

changelogs/unreleased/28229-pipelines-loading-icon.yml

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-title: Centers loading icon vertically and horizontally in pipelines table in commit
-  view
-merge_request:
-author:

changelogs/unreleased/28236-browse-button-dropping.yml

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-title: Increase right side of file header to button stays on same line
-merge_request:
-author:

changelogs/unreleased/28247-timeloops-bug.yml

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-title: Only run timeago loops after rendering timeago components
-merge_request:
-author: